What is a pixel in image processing?

If you ever decide to digitize your old photos (which you should do, by the way), one term you will constantly hear is ‘pixel’. An extremely important aspect of photo processing is the concept of a pixel. The amount of money you will have to pay for the digitizing service will depend on how many pixels per unit area your photos have. So, what is a pixel in image processing?

Pixel is the lowest unit of an image that possesses any information. It is a two-dimensional part of the photo that can either be round or square. Each of these units represents the image, so the more pixels are there in an image, the more information will be there in the image.

Let’s dive deeper into the concept of pixels and see how it affects photo quality.

How to define pixel and resolution?

When people digitize their photos, the properties of digitized photos are not like the physical ones. Unlike physical photos, which are printed on paper, digitized photos have no such base. Instead, they are composed of tiny parts of photos that have smaller pieces of data from the original photo. 

These small digital parts of digitized photos are called pixels. ‘Pixel’ is a word that is derived from the words ‘Picture’ and ‘Element’. Pixels are not devoid of color, as they all have either three or four colors each. 

Now, you might think, how big are the smallest units of photos actually, or what is pixel size? Usually, a pixel is 1/96th of an inch. But, if the resolution of the photo is high, the pixel size will be smaller, and in the case of a low-resolution photo, the size will be larger. 

Speaking of resolution, it is another term you often hear when talking about images. But what is pixel resolution? Well, you can explain the resolution in a couple of ways. First, you can explain it by saying the resolution is the total number of pixels in a photo.

For example, if a photo has 1920 pixels in a row and 1080 pixels in a column, then the resolution will be 1920×1080 = 2073600 pixels. But expressing the resolution in such a big number can be quite tricky. This is why the resolution of a photo is denoted by the term megapixel.

A megapixel is what you get when you divide the number of pixels in a photo by 1 million. So, 1 megapixel = 1000000 pixels. By this definition, the aforementioned photo’s resolution will be 2.07 megapixels. 

Another way to denote resolution is by saying how many pixels are there in a unit area. For example, a photo that has 300 pixels per inch will be of a lower quality than a photo that has 4000 pixels per inch, since every unit area of the second photo contains more information than the first. This will come in very handy during the processing of images and manipulation of the said image. 

Now, why is the idea of resolution so important? For instance, when you buy a camera or are discussing one, the camera with the higher megapixels will always take better photos than a camera with lower megapixels. For example, if there are two cameras of 12 and 5 megapixels respectively, the former will take a much better photo than the latter.#

Because the photos taken by the second camera can not have more than 5 megapixels in them, the ones taken by the 12-megapixel camera will have a lot more pixels, and in turn information in them. So their resolution will also be higher.

Why processing pixels is important in digitizing photos?

There are a ton of photos in our homes that are not only occupying a lot of space that could’ve been used otherwise but are also being damaged as they are just sitting there. As the photos get older, they get more fragile and prone to damage. That’s why it is a great idea to digitize them to save both the photos and space.

Now, when physical photos are concerned, there are three types of them just sitting around in our homes: printed photos, negatives, and slides. While slides and negatives are the original versions of the photo, printed ones are duplicates. As a result, the printed ones have a lot less information than the original ones.

So when you digitize them, the digitized versions of the slides and negatives are of much better quality than the printed ones. For instance, printed photos have only two resolutions, 300 DPI (Dot per Inch) and 600 DPI. In comparison, slides and negatives can be digitized in formats that can have up to 4000 DPI. 

There are two sides to these. First, the quality of the photos will be much different. Scanned prints will have less quality than scanned slides because of the lack of information in them. Second, the price of digitizing will also vary according to the resolution.

We, at digitized media, charge between £0.08 and £0.16 per photo for 300 DPI photos, between £0.12 and £0.20 for 600 DPI photos, and our special 1200 DPI photos cost between £0.20 and £0.28, depending on the number of photos you want to scan. You can see that the price rises as the quality of the image also rises.

On the other hand, for scanning slides, we charge between £0.33 to £0.55 per slide, depending on the number of slides. The cost of scanning negatives is similarly higher than that of scanning prints. As you can see, due to the difference in resolution, the cost of digitizing prints, slides, and negatives varies a lot. 

When digitizing your photos, you have to keep this in mind. We would suggest that if you have access to both prints and slides/negatives, and budget isn’t an issue, go for scanning slides or negatives to get a much better result. 

What is the difference between PPI and DPI?

Notice how we denoted the resolution of the photos above as Dot per Inch, or DPI instead of Pixel per inch or PPI? Although the basic concept and measurement of DPI and PPI are the same, there is a slight difference between them. 

DPI is used to denote how many dots are there in a square inch of area in a printed photo, while PPI is the number of pixels in a square inch area. The more the DPI is, the better the resolution of the prints is and the same can be said about PPI. That’s the reason these two terms are used interchangeably. 

Does an image’s resolution have any effect on the file size?

The resolution of an image has a large part in determining what the size of a digitized image file will be. The more pixels are there in a photo, the higher will be its resolution. The higher the resolution, the more information will be there in it. The more information is there in a photo, the larger the file size will be.

So, a photo with a higher resolution will always have a bigger file size than a photo with a lower resolution. If there are two photos, one with 3.1 megapixels and the other with 6 megapixels, the latter one will have the bigger file size. 

Final Words

Whenever people want to digitize their photos and have any discussions about digitized photos, they come across the word ‘Pixel’. If someone is not familiar with the concept, it is only natural for them to ask, “What is a pixel in image processing?” Once you know what a pixel is and how much it is important when it comes to digitizing your photo, you can understand how this business works and also will be able to make smarter decisions. 

FAQs

1. What do pixel colors depend on?

The color of pixels depends on the number of bytes of the said pixel. If the pixel has 8 bytes, it will have 256 colors. For a pixel of 16 bytes, the number of colors goes up to 65,536. For a 24-byte pixel, the number of colors is 16,777,216. But human eyes can only distinguish between 10 million colors, so we can’t see that many colors.

2. Is pixel 2D or 3D? 

A pixel is a 2D grid that contains a small piece of information from a picture. It must be noted that pixels only exist on a 2D plane, the data used to encode a photo is not necessarily 2-dimensional. 

3. In what formats can you digitize a photo?

Scanned photos can be saved in quite a few formats. The most common formats of digitized photos are JPEG, GIF, and PNG. The more uncommon formats are TIFF, PSD, BMP, and RAW.